U.S. Pat. No. 7,524,192 B2 describes 7P and 4P sockets in one socket housing with 2 covers fixed with one common axle or hinge pin and a common biasing element (spring) to close both covers. In this embodiment, one cover can only be opened if the other cover is closed. However, it is a disadvantage that the two covers open in different rotation directions. Further, the blocking function of the covers cannot be deactivated if a socket without this blocking function is desired.
In the U.S. Pat. No. 6,447,302 an adapter configured as a master and slave system is described where 7P and 4P sockets are provided in one socket housing with 2 covers. Both covers open in same direction, toward the top, while the hinge pin axles are adjacent. Only the 7P has a bias spring to close cover while the 4P has no spring. Further, no blocking of the covers is provided.